diff --git a/webmidi/idlharness.https.window.js b/webmidi/idlharness.https.window.js
index 1474b3845af1dd..fabc836fdba582 100644
--- a/webmidi/idlharness.https.window.js
+++ b/webmidi/idlharness.https.window.js
@@ -11,19 +11,23 @@ idl_test(
   ['html', 'dom', 'permissions'],
   async idl_array => {
     idl_array.add_objects({
-      MIDIAccess: ['access'],
-      MIDIInputMap: ['inputs'],
-      MIDIOutputMap: ['outputs'],
+      MIDIPort: [],
+      MIDIMessageEvent: [
+        'new MIDIMessageEvent("type", { data: new Uint8Array([0]) })'
+      ],
       MIDIConnectionEvent: ['new MIDIConnectionEvent("type")'],
     })
 
     self.access = await navigator.requestMIDIAccess();
     self.inputs = access.inputs;
+    self.outputs = access.outputs;
+    idl_array.add_objects({ MIDIInputMap: ['inputs'] });
+    idl_array.add_objects({ MIDIOutputMap: ['outputs'] });
+    idl_array.add_objects({ MIDIAccess: ['access'] });
     if (inputs.size) {
       self.input = Array.from(access.inputs.values())[0];
       idl_array.add_objects({ MIDIInput: ['input'] });
     }
-    self.outputs = access.outputs;
     if (outputs.size) {
       self.output = Array.from(access.outputs.values())[0];
       idl_array.add_objects({ MIDIOutput: ['output'] });